The present invention relates to continuous methods for shaping the surface of a slab of compressible or cellular polymer material, such as polyurethane foam, by cutting portions of the material from the slab with a blade after the slab has been compressed between a compression roller and a support surface.
Several methods and apparatus for cutting slabs of cellular polymer materials have been disclosed in the prior art. For example, U.S. Pat. No. 4,700,447 to Spann discloses convolute-cutting slabs of polyurethane foam by compressing a slab or pad of foam between a pair of rolls with opposed spaced projecting fingers arranged in a pattern and cutting the foam with a saw blade transversely just as it emerges from the rolls. The cut slab is then separated into two pads each with convolute-cut surfaces forming a series of peaks separated by valleys. The valleys formed on one pad are formed by slicing away foam which becomes a mating peak or projection on the other pad. Spann then shaves the peaks to form a more planar top surface. As noted in Spann, convolute cutting alone produces only rounded peaks and rounded valleys, and it is difficult, if not impossible, to produce a cut surface with peaks having substantially flat top surfaces or with recesses having substantially straight side walls. The convolute usually is intended to form the classic symmetrical and repeating "egg crate" pattern of peaks and valleys. To achieve a planar upper surface at other than the recessed portions, the tops of the peaks must be cut or shaped in a second step.
Compressible cellular polymer materials may also be cut using a hot wire cutter. A slab of such material is cut by moving the slab relative to one or more hot wires as shown, for example, in U.S. Pat. No. 4,683,791 (Demont). Only straight cuts in regular or symmetrical patterns may be formed using a hot wire cutter. See also U.S. Pat. No. 4,915,000 (MacFarlane) and U.S. Pat. No. 5,573,350 (Stegall).
Shapes may be cut into the surface of a slab of cellular polymer material using a punch cutting apparatus, such as disclosed in U.S. Pat. No. 5,299,483 (BerFong). A block of the cellular material is pressed against a template so that a portion of the material is forced through an opening in the template. The exposed material is then cut by a blade and removed, leaving a recess or cavity in the slab. This method cuts one block of material at a time, and only one surface at a time.
U.S. Pat. No. 4,351,211 (Azzolini) compresses a block of foam material against a template or die having an aperture therein using a pair of plates with concave and convex portions. The compressed foam is transversely cut along the template as it is held between the plates. More complex cut regions may be obtained than when using a template without the plates with raised and depressed portions, but only one block is cut at a time. Other template or pattern cutting methods are shown in U.S. Pat. No. 3,800,650 (Schroder) and U.S. Pat. No. 3,653,291 (Babcock).
The surface of a cellular polymer material may be shaped by molding or embossing, as opposed to cutting U.S. Pat. No. 4,383,342 (Forster), for example, discloses injecting the foam-forming composition in a mold cavity. After sufficient curing time, the individual foamed article is removed from the mold. Other one-shot molding techniques are known to persons of skill in the art. The molded cellular polymer product generally forms a tough skin at the surfaces that were in contact with the mold.
Continuous and semi-continuous molding processes are also known. These processes have the same drawbacks associated with one-shot molding techniques. For example, U.S. Pat. Nos. 4,128,369 and 4,290,248 (Kemerer, et al.) disclose an apparatus and method for impression molding thermoplastic products. The thermoplastic material in a liquid state is injected between compressed traveling belt molds. As the belt molds travel away from the point of introduction of the thermoplastic, they are cooled, which in turns cools the thermoplastic material. The hardened molded thermoplastic material is removed from between the belts to form the finished product. Kemerer does not show a method for cutting or shaping a cellular polymer material, such as polyurethane foam.
A method of embossing a foam surface using a patterned metallic embossing belt or band is shown in U.S. Pat. 4,740,258 (Breitscheidel). The foam is heated and then pressed against the embossing belt. The belt is removed after the foam surface cools. The embossed surface by design has a hardened skin. No method for cutting or shaping the foam is disclosed.
U.S. Pat. No. 5,534,208 (Barr) discloses a continuous rotary method for surface shaping synthetic foams in which the foam is compressed between a compression roller and a die roller having raised and recessed portions. The portions of the foam extruded into the recesses in the die roller are cut away. The compressed foam portions return to an uncompressed state after passing through the rollers. As a result, a mirror-image pattern to the pattern on the surface of the die roller is cut on the surface of the foam. The diameter of the die roller limits the length of the shaped foam article that may be formed.
The prior art does not disclose a continuous method for shaping a compressible or cellular polymer material by cutting to form recesses of various depths and various symmetrical and nonsymmetrical shapes. Nor does the prior art disclose a method for shaping a slab of compressible or cellular polymer material of unlimited length using a movable patterned platform, such as an endless belt, as the template for cutting the surface of the slab. Nor does the prior art disclose a method for forming a profile cut product without the hardened skin or hard spots associated with molded or embossed products.